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If you think about cold sores, words that pop into your head probably include "unsightly," "painful," and "contagious." There's good reason for that. Also known as fever blisters, cold sores also indicate that you've contracted a viral infection. The virus that causes cold sores is herpes simplex 1, or HSV-1, a cousin to the herpes simplex virus 2 that causes most genital herpes. More than half of all Americans are infected by type 1 herpes by the time they're in their twenties, so "common" might be another apt description for cold sores.

Cold Sore Contagion

Cold sores seem to spread easily, but just how contagious are they? “Very,” said dermatologist Mark Kaufmann, MD, an associate clinical professor of dermatology at the Icahn School of Medicine at Mount Sinai in New York City. About 10 percent of people who are infected with type 1 herpes simplex will develop a cold sore within one to two weeks.

Cold sores are most contagious when they rupture — when fluid seeps out of the sores. But they're actually contagious from the time you first feel cold sore symptoms, like tingling or itching around your mouth, until they're completely healed and gone. Just because the cold sore is scabbed over doesn’t mean it's no longer contagious. Eat, talk, smile, and your scab can break and the fluid can leak out.

How to Avoid Spreading Cold Sores

Here’s how you can avoid spreading cold sores to others:

Don’t pucker up. You can spread cold sores simply by getting up close and personal with your loved ones. Give a kiss anywhere, but especially the mouth, and you could easily pass on the virus.

Don’t share. If you put it in your mouth, don’t share it. You can easily pass on your cold sores by sharing food, eating utensils, drinking straws, cups, and glasses. That goes for lip balm or lipstick, toothbrushes, and razors as well. Even towels you use to dry your face can be harbingers of the virus when you have a cold sore. “The virus can survive for a little while on non-living items like these,” Dr. Kaufmann explained. Tell your friends and family: Get their own if they don’t want your cold sore.

Don’t touch. “We touch our faces about a million times a day,” Kaufmann said. But, every time you touch your cold sore with your hands, you could be spreading the virus. If the virus gets on your hands and you don’t wash them right away, it could spread to whatever you touch next — your keyboard, the phone, a doorknob. “That’s why you should use a hand sanitizer a lot when you have cold sores,” he said.

Don’t engage in oral sex. The same virus that causes cold sores also can be responsible for blisters and sores in the genital area. When you have a cold sore, you don’t want your mouth to come in contact with your partner’s genitals.

Use hot water. Wash any items you use in boiling hot water to kill the virus.

Avoid triggers. One of the best ways to avoid spreading cold sores is to avoid getting them in the first place. Some things that may trigger an outbreak are stress, sunburn, fever, and illness. Apply sunblock to avoid getting a sunburn and lip balm to prevent your lips from getting too dry. Ease stress with meditation and other relaxation techniques.

Consider cold sore treatment. Left untreated, it can take a week or more for cold sores to run their course. Over-the-counter creams can speed healing somewhat. You also can ask your doctor for a prescription medication. A study in the journal Postgraduate Medicine shows that acyclovir and hydrocortisone cream (Xerese) shortens the time it takes for cold sores to heal. Apply a cold sore treatment with a cotton-tip swab to prevent it from spreading to other parts of your body. If you treat your cold sore and it heals faster, you'll be contagious for a shorter time. A cool compress or ice may help ease the pain. Never squeeze or pick at your cold sore because that will delay healing.

Many people get warning signs that a cold sore is about to appear, Kaufmann said. So as soon as you feel that familiar tingling, itching, or skin sensitivity, going into contagion prevention mode can help keep it from spreading to others.